Hydrocarbon containing fuels such as gasoline are the most common power source for internal combustion engines. Gasoline must be carried by the vehicle, usually in a fuel tank. Heretofore fuel tanks have been manufactured from metal. More recently however, much work has been done on fuel tanks made from plastic resins, typically, polyethylene. Polyethylene is a very suitable material for making fuel system components such as tanks in that it is readily moldable using blow molding techniques. However, it has been determined that fuel vapour can permeate through the wall of the fuel system component such as a fuel tank when the wall is manufactured solely from polyethylene. In order to provide suitable anti permeation characteristics, more complex wall structures for such fuel system components have been developed. In our co-pending patent application Ser. No. 09/192,295, filed Nov. 17, 1998, now abandoned, the disclosure of which is herein incorporated by reference, there is a discussion of a multi-layer fuel conduit. Such conduits are readily manufacturable using blow molding techniques.
Plastic molded fuel tanks have now been proven to be commercially acceptable on incorporation of some means to control permeation. Typically, the permeation can be controlled by barrier layers such as a layer of ethylene vinyl alcohol copolymer (EVOH) which is incorporated into a multi-layer parison and wall structure. Typically, in order to adhere the EVOH layer, adhesive is supplied to either side of the EVOH barrier layer as the barrier layer is extruded from the extrusion head. Typically, the adhesive attaches the EVOH layer to an outer layer of polyethylene and an inner layer of polyethylene. Either or both of the polyethylene materials may include either virgin material or scrap, reground, polyethylene material or combinations of the two. Where required by the conditions, the inner layer of the fuel system component may also be modified so as to conduct electricity. This helps provide an electrical path to bleed off static electricity which might be generated in or around the fuel stored in the fuel system component. All of the various layers are simultaneously extruded through a multi-channel extrusion head to produce a parison ready for molding.
In the blow molding technique, a parison is extruded from an extrusion head. The parison is normally allowed to hang vertically from the extrusion head as the correct amount of parison to make the desired part is extruded. The parison is placed between the open portions of a blow molding mold. The blow molding mold is then closed around the parison and the parison is pinched off. A convenient structure, typically a blow molding needle, pierces the wall of the parison and blowing gas under pressure is introduced into the interior of the parison. The parison which at that stage is hot and still quite flowable, is expanded outwardly and the shape of the cavity in the blow mold determines the exterior configuration of the blow molded part.
Using the blow molding techniques and barrier incorporation technology discussed above, fuel system components may be manufactured which contain barrier layers which significantly inhibit the permeation of hydrocarbon vapours. In many instances however, other fuel system components may be attached to items such as fuel tanks. Many fuel tanks have pipe nipples, flanges or other like elements which are attached to the tank so as to couple the tank to conduits, vapour return lines and the like. These other fuel system components are then attached to the fuel tank, typically surrounding an aperture so as to permit fluid communication with the interior of the tank.
Although polyethylene is easily moldable, polyethylene deflects under load and is known to creep. Thus, if a hose or like component is attached to an underlying polyethylene component by a hose clamp or the like, the polyethylene material will creep over time under the stress induced by the pipe clamp. This then leads to potential looseness in the fitting between the pipe nipple and the conduit overlying the pipe nipple. This problem has been recognized in U.S. Pat. No. 5,443,098, Rasmussen. In the Rasmussen patent, it is suggested that a portion to which a conduit is to be affixed be manufactured from a material such as polyamide which has a much higher creep resistance. While this answers the problem of creep, it introduces another problem. Polyamide is not easily weldable directly to polyethylene. Thus, in order to match the polyamide based component to the fuel tank, the Rasmussen patent suggests the pipe nipple should be manufactured from a two part structure. The second part of the structure as outlined in the Rasmussen patent is made from a non-reinforced modified polyethylene. The modified polyethylene product forms a diffusion bond with the polyamide and may also be welded to the polyethylene outer layer of a fuel tank. Other components may also be attached to a fuel tank using such a layer of polyethylene or modified polyethylene chosen to simplify welding to the tank structure. Typically the form of the component for welding is in the nature of a flange member. If creep is not an issue in the particular component, then the entire member may be made from a modified polyethylene or the flange may be attached to a member made of some other substance.
The flange made of polyethylene or modified polyethylene provides another path for fuel vapour permeation. Thus, while polyamide products inherently exhibit fuel vapour permeation characteristics which are satisfactory, flange members which may be used in association with polyamide containing products provide a possible escape route for fuel vapours permeating through the flange.
It would be desirable to create a flange member which would help in inhibiting fuel vapour permeation from a fuel tank system. Such a flange member could then be used in association with fuel tanks and other components or portions of components which may otherwise have sufficient and acceptable fuel vapour inhibition characteristics.